Is a Contract without consideration valid?

In four instances a Pakistani contract is valid even without consideration is valid. Firstly, where agreement is in writing and is based on natural love and affection, secondly, where agreement is to compensate person who has performed some act voluntarily for promisor or done something which promisor would have been legally obliged to do, thirdly, where it is promise in writing to pay time-barred debt, and, lastly, where there is contract of agency.